Microphone having a variable unidirectional characteristic



0d. 27, 1970 wgm TN v 3,536,862

MICROPHONE HAVING A VARIABLE UNIDIRECTIONAL CHARACTER'ISTIC Filed Aug.9, 196? 4 Sheets-Sheet 1 FIG? Hypercardl'ald FIG. 3

\ ercard/b/d Y INVENTOR Belem/ARI) NElA/GARTMEK ATTORNEYS Oct. 27, 1970WEINGAR NEFE 3,536,862

MICROPHONE HAVING A VARIABLE UNIDIRECTIONAL CHARACTERISTIQ Filed Aug. 9,1967 4 Sheets-Sheet 2 I INVENTOR BiRM/IHKD HEM/641971146? ATTORNEYS L1970 B. WEINGARTNER 3,536

' MICROPHONE HAVING A VARIABLE UNIDIRECTIONAL CHARACTERISTIC Filed Aug.9, 1967 4 Sheets-Sheet 5 INVENTOR H m/ MD Meme/WW5? WQMMM LL ATTORNEYSOct. 27, 1970 w m 'j- 7 3,536,862

MICROPHONE HAVING A- VARIABLE UNIDIRECTIONAL CHARAOTERISTIC Filed Aug.9, 1967 4 Sheets-Sheet 4 INVENTOR Beam/m0 we ml 6A3TA167 ATTORNEYSUnited States Patent 3,536,862 MICROPHONE HAVING A VARIABLEUNIDIRECTIONAL CHARACTERISTIC Bernhard Weingartner, Vienna, Austria,assignor to Akustische u. Kino-Gerate Gesellschaft m.b.H., Vienna,

Austria Filed Aug. 9, 1967, Ser. No. 659,445 Claims priority,application Austria, Aug. 19, 1966, A 7,930/66 Int. Cl. H04r 1/34 US.Cl. 179-121 14 Claims ABSTRACT OF THE DISCLOSURE A microphone having acardioid directional characteristic, when the sound detour through soundinlet openings communicating with forward and rear diaphragm faces, asmeasured on the outside of the microphone, has a predetermined length,is provided with a deflecting member mounted on the outside of themicrophone between the sound inlet openings and adapted selectively tomodify the length of the sound detour.

BACKGROUND OF THE INVENTION There are known microphones which have anomnidirectional (spherical) characteristic, microphones which have aunidirectional (cardioid) characteristic and microphones which have abidirectional (figure eight-shaped) characteristic. The optimumcharacteristic for any particular application will depend on theconditions of use. Unidirectional microphones are preferable in mostcases. The generation of a unidirectional characteristic can beexplained most conveniently by reference to the principle ofsuperposition.

If a microphone having an omnidirectional characteristic and amicrophone having a bidirectional characteristic are superposed, forexample in a suitable electric circuit, the resulting system will have aunidirectional characteristic. If the contributions of the twomicrophones are the same (50% omnidirectional charact ristic and 50%bidirectional characteristic) an ideal cardioid directionalcharacteristic will be obtained. If the bidirectional contribution is75% and the omnidirectional contribution is 25%, a hypercardioidcharacteristic will be obtained and, a ratio of 63% bidirectionalcharacteristic to 37% Omnidirectional characteristic results in asupercardioid characteristic.

Depending on the conditions of use, each of these three unidirectionalcharacteristics has its special advantages. The pure cardioidcharacteristic results in a wide useful sound receiving angle, and in agood supression of direct sound which is incident from the rear (180).The hypercardioid characteristic results in a cancelling at an angle 11of about 110, and in the optimum suppression of diffused sound(reverberation). On the other hand, it results in a narrower receivingangle and a reduced suppression of sound incident fro-m the rear. Thesupercardioid characteristic is a compromise of the two characteristicsjust discussed.

Many arrangements have been suggested to provide for a variation of thedirectional characteristic by a control of the omnidirectional orbidirectional contributions. It is also known that a simplesuperposition of the acoustic elements of the omnidirectional system orof the bidirectional system enables the generation of a resultingunidirectional characteristic with only one transducer system (onediaphragm).

In a dynamic microphone, the acoustic elements of thepressure-responsive system, having an omnidirectional characteristic,comprise a space which is closed from the Patented Oct. 27, 1970 iceoutside air and connected by a frictional resistance to a relativelyshallow air chamber behind the diaphragm. On the other hand, theacoustic elements of the bidirectional system consist essentially of asuitably sized opening leading from the air chamber into the free rearsound field. As a result, the diaphragm actuating force of thepressure-responsive system is proportional to the sound pressure infront of the diaphragm, whereas the actuating force generated by thebidirectional system is proportional to the difference between the soundpressure before the diaphragm and the sound pressure behind thediaphragm. This pressure difference is approximately proportional to thedistance between the center of the forward side of the diaphragm and therear sound inlet, provided that this distance is much smaller than thewave length of the sound to be transmitted.

SUMMARY OF THE INVENTION This invention relates to microphones having apure cardioid characteristic and, more particularly, to such amicrophone which can be converted ina simple manner into one havingeither a supercardiod characteristic or a hypercardioid characteristic.

In accordance with the invention, a microphone having a pure cardioidcharacteristic, or equal omnidirectional and bidirectionalcontributions, is provided with means whereby the sound detour isvariable, the variation being effected by the provision of deflectingmember in the form of a disk or sleeve on the exterior or outside of themicrophone. Preferably, the deflecting member is in the form of afrustum of a cone. The deflecting member is located between the soundinlet opening, communicating with the forward face of the diaphragm, andthe sound inlet opening communicating with the rear face of thediaphragm.

The deflecting member can be made detachable, adjustable in size,adjustable in shape, or to have any tWo or more of thesecharacteristics.

In one form of the invention, the deflecting member may be formed withopenings, apertures, slots or the like, which can be selectively closedby suitable mechanisms, the size of the openings or the like beingpreferably infinitely adjustable, in the manner of a variable orifice.

An object of the invention is to provide a microphone having a purecardioid characteristic with means whereby the characteristic may bechanged into a supercardioid characteristic or a hypercardioidcharacteristic, selectively.

Another object of the invention is to provide such a microphoneincluding means for varying the sound detour between the sound inletopening communicating with the forward face of the diaphragm and thesound inlet opening communicating with the rear face of the diaphragm.

A further object of the invention is to provide such a microphone inwhich such means comprises a deflecting member in the form of a disk orsleeve and mounted on the exterior or outside of the microphone.

Still another object of the invention is to provide such a deflectingmember in the form of a frustum of a cone.

A further object of the invention is to provide such a member which isdetachable.

Yet, anotherobject of the invention is to provide such a deflectingmember which'is adjustable in size or shape or both.

Yet, another object of the invention is to provide such a deflectingmember with openings or other forms of apertures Whose areas arepreferably infinitely adjustable or variable by suitable mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS For an understanding of the principlesof the invention, reference is made to the following description oftypical embodiments thereof as illustrated in the accompanying drawings.

In the drawings:

FIGS. 1, 2 and 3 are graphical representations of, respectively, anideal cardioid directional characteristic, a hypercardioid directionalcharacteristic and a supercardioid directional characteristic;

FIG. 4 is a sectional view of a microphone embodying the invention andillustrating the basic functioning of the deflecting member;

FIG. 5 is a view, similar to FIG. 4, illustrating the deflecting memberas formed with apertures therethrough;

FIG. 6 is a top plan view of FIG. 5; and

FIG. 7 is an elevation view, partly in section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1, 2and 3, if the contribution of two microphones are the same, that is, 50%omnidirectional characteristic and 50% bidirectional characteristic, anideal cardioid directional characteristic will be obtained as shown inFIG. 1. If the bidirectional contribution is 75% and the omnidirectionalcontribution is 25%, a hypercardioid directional characteristic will beobtained as shown in FIG. 2. If the bidirectional contribution is 6 3%and the omnidirectional contribution is 37%, a supercardioidcharacteristic will be obtained as shown in FIG. 3.

In FIG. 4, a capsule 1 of a dynamic microphone is illustrated as havinga forward sound inlet 2 and a rear sound inlet 3. A diaphragm 4 isillustrated in broken lines, and a pressure chamber 5 communicates withthe rear of the capsule. The sound detour d representing the externaldistance between the forward sound inlet 2 and the rear sound inlet 3,determines the magnitude of the actuating pressure difference, andconsequently determines the bidirectional contribution. The acousticelements of the microphone system are so dimensioned that sound detour dresults in a cardioid directional characteristic.

When a deflecting disk 6 is applied to the microphone, in accordancewith the invention, the sound detour between the forward sound inlet 2and the rear sound inlet 3 is increased to (1 As a result, the pressuredifference and the bidirectional contribution will also increase so thatthe microphone system, having a cardioid characteristic, is converted bydeflecting disk 6 into a microphone having a predominating bidirectionalcontribution. More particularly, the microphone is converted into onehaving a supercardioid or hypercardioid characteristic, depending on thesize of the disk. To avoid irregularities in the frequency response dueto the dynamic pressure eifect or due to diffraction effects of disk 6,the latter is preferably frusto-conical in form.

In the embodiment of the invention shown in FIGS. 5 and 6, thedeflecting member 6 is formed with openings 7 whose area is infinitelyvariable between a fully opened condition and a fully closed condition.Disk 6 is preferably formed of plastic composition material. A closingring 8 is rotatably mounted in a groove 9 of disk 6', and preferablycomprises punched sheet metal. Closing ring 8 is rotatable by adjustinglever '10, and has openings 11, corresponding to opening 7, which enablean infinitely variable opening and closing of openings 7.

The arrangement shown in FIGS. 5 and 6 is capable of providing threedifferent sound detours and three different bidirectional contributions,namely d without the deflecting disk d with the deflecting disk havingthe openings 7 closed and d with the deflecting disk having the openings7 open. The detours are dimensioned so that al results in a cardioidcharacteristic, d in a hypercardioid characteristic and d in asupercardioid characteristic.

A practical form of microphone embodying the invention is illustrated inFIG. 7. In FIG. 7, microphone capsule 1 is incorporated in a housing 12provided with a cap 13. Sound enters in front through protective screen14 and enters at the rear through slots 15 in cap 13. Electricalconnections are established by cable 16, and the deflecting disk 6, inaccordance with the invention, is adapted to be fitted to cap 13.

With a view to a pleasing appearance, the deflecting disk may beprovided in different shapes, such as circular, elliptical, orpolygonal. Type references and the name of the manufacturer may beprovided on the deflecting member 6, which preferably is formed ofplastic composition material.

As a further feature of the invention, deflecting member 6 may be usedas a foot or the like for supporting the microphone of the table. Inthis case, it may be desirable to provide a ring 17 of elastic materialin a groove formed at the periphery of the deflecting disk, as best seenin FIGS. 7 and 8.

The deflecting member may be flatter than shown in the drawings or maymore closely resemble a sleeve. While its contour is preferablycircular, elliptical or polygonal, alternatively the deflecting disk mayhave a star-shaped contour or the like. Also, the size of the deflectingmember may be made variable, in the manner of an iris diaphragm such asused in photography, but arranged to vary the outside diameter of thedeflecting member.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. A microphone, having a variable unidirectional characteristic,comprising, in combination, a capsule containing electro-acoustictransducer means having forward and rear diaphragm faces; means definingforward and rear sound inlet openings communicating with said forwardand rear diaphragm faces, respectively; a sound detour representing theexternal distance between said inlet openings as measured on the outsideof said microphone, said microphone having a cardioid directionalcharacteristic in response to sound waves entering through said soundinlet openings when said sound detour has a predetermined length; and asound path deflecting member mountable on the external periphery of saidcapsule between said sound inlet openings to modify selectively thelength of said sound detour to obtain differently defined unilateraldirectional characteristics for said microphone.

2. A microphone, as claimed in claim 1, in which the size of saiddeflecting member is selectable to select the desired length of saidsound detour.

3. A microphone, as claimed in claim 1, in which said transducer meanscomprises a single diaphragm having said forward and rear faces.

4. A microphone, as claimed in claim 1, in which said deflecting memberis disengageably mounted on said microphone; said sound detour havingsaid predetermined length When said deflecting member is removed fromsaid microphone, and having a length greater than said predeterminedlength when said deflecting member is mounted on said microphone.

5. A microphone, as claimed in claim 1, in which the external peripheryof said deflecting member is in the form of a closed plane geometricfigure, said deflecting member forming a support for said microphone ona base.

6. A microphone, as claimed in claim 1, in which said deflecting memberhas a form of a flat truncated cone.

'7. A microphone, as claimed in claim 1, in which said deflecting memberhas a frictional fit on said microphone.

8. A microphone, as claimed in claim 1, in which said deflecting memberis formed with sound passage apertures therethrough.

9. A microphone, as claimed in claim 8, in which said deflecting memberincludes adjusting means selectively operable to vary the areas of saidapertures to vary the length of said sound detour.

10. A microphone, as claimed in claim 9, in which said adjusting meansis continuously adjustable.

11. A microphone, as claimed in claim 5, in which said deflecting memberhas an elliptical external periphery.

12. A microphone, as claimed in claim 5, in which said deflecting memberhas a polygonal external periphery.

13. A microphone, as claimed in claim 5, in which said deflecting memberincludes a ring of elastic material extending around its externalperiphery and projecting at least partly from said external periphery.

14. A microphone, as claimed in claim 1, in which said deflecting memberis substantially disk-shaped.

References Cited UNITED STATES PATENTS 2,787,671 4/1957 Grosskopf179-121 10 KATHLEEN H. CLAFFY, Primary Examiner T. L. KUNDERT, AssistantExaminer

